TITANIFEROUS    IRON    ORE    OF    IRON    MOUNTAIN,  WYOMING.       207 
foothills  1  mile  from  the  eastern  border  of  the  pre-Cambrian  complex, 
in  sees.  22,  23,  26,  and  27,  T.  19  N.,  R.  71  W.,  is  reached  from  Iron 
Mountain  station  by  a  wagon  road.  Chugwater  Creek  passes  in  a 
gorge  through  the  iron  ore  body. 
Beside  this  main  body  of  the  magnetic  iron  minor  masses  occur  in 
the  pre-Cambrian  rocks  in  a  belt  which  is  reported  to  extend  from 
Horse  Creek  to  Sibylee  Creek,  a  distance  of  20  miles.  This  belt,  which 
courses  a  little  east  of  north  and  west  of  south,  is  in  places  5  miles  wide. 
Iron  Mountain,  a  rugged  ridge  from  300  to  600  feet  wide  and  1J 
miles  long,  rises  sharply  from  the  anorthosite  hills  to  the  east  and  the 
rolling  pre-Cambrian  uplands  to  the  west.  Its  ragged  top  presents  a 
marked  contrast  to  the  regular  hogbacks  of  the  foothill  sedimentary 
rocks. 
The  iron  was  first  noticed  by  Capt.  Howard  Stansbury,  U.  S.  Army, 
on  September  30,  1850,  when  he  was  in  camp  on  the  banks  of  Chug- 
water Creek,  on  his  way  to  Great  Salt  Lake.  He  found  along  the 
banks  of  the  stream  and  in  the  adjacent  hills  "immense  numbers  of 
rounded  black  nodules  of  magnetic  iron  ore,  which  seemed  of  unusual 
richness."  a  In  1866  F.  V.  Hayden  visited  the  mountain  itself.  The 
greater  portion  of  the  main  deposit  passed  into  the  hands  of  the  Union 
Pacific  Railroad  as  a  part  of  the  land  granted  to  it  in  1862.  In  1872 
a  wagon  road  was  built  to  the  deposit,  prospectors  rushed  in,  and  the 
whole  countryside  was  staked.  In  the  following  year  a  post-office, 
Iron  Mountain,  was  established  at  the  base  of  the  iron  ridge,  but  was 
abandoned  in  1874.  Eight  or  ten  years  ago  the  Colorado  Fuel  and 
Iron  Company  employed  15  teams  for  several  months  in  hauling  ore 
from  the  mountains  to  the  railroad,  whence  it  was  shipped  to  their 
smelters  at  Pueblo.  The  work  was  suddenly  abandoned,  however, 
although  the  same  company  is  reported  to  have  made  a  small  ship- 
ment four  years  ago.  In  1905  and  1906  the  main  ore  body  was  visited 
by  a  number  of  surveying  corps,  and  the  Colorado  Land  and  Iron 
Company  is  said  to  have  located  claims  between  Chugwater  and 
Sibylee  creeks. 
GEOLOGY. 
The  pre-Cambrian  complex  near  the  large  dike  of  iron  ore  at  Iron 
Mountain  consists  of  three  granular  igneous  rocks — an  anorthosite,6 
the  iron  ore,  and  a  granite.  The  anorthosite  is  the  oldest  of  these 
and  is  cut  by  dikes  and  lenticular  masses  of  iron  ore  and  granite.  The 
relative  ages  of  the  iron  ore  and  granite  was  not  certainly  determined, 
since  exposures  are  poor  where  the  two  rocks  are  close  together.  All 
the  available  evidence,  however,  indicates  that  the  iron  ore  is  older 
than  the  granite. 
a  Stansbury,  Howard,  Exploration  and  survey  of  the  valley  of  the  Great  Salt  Lake  of  Utah,  Wash- 
ington, D.  C,  March,  1851. 
b  Anorthosite  is  a  granular,  wholly  crystalline  igneous  rock,  composed  essentially  of  striated  Jirrie- 
soda  feldspar,  usually  labradorite. 
